This report presents an assessment of relationships between hypolimnetic dissolved oxygen depletion in Lake Simcoe and its morphometric, nutrient loading and other physiochemical and biochemical attributes (e.g., temperature; water column oxygen demand, WCOD; sediment oxygen demand, SOD). The objectives of this work were: i) to analyse available data to attempt to establish whether the dissolved oxygen depletion in Lake Simcoe has changed as a result of phosphorus control programs, and ii) to identify other work required to ensure that the most important variables influencing hypolimnetic oxygen depletion are measured.